1. Field of the Invention
The present invention is related to an ophthalmic examination apparatus, more particularly a contact eye imaging camera which uses the miniature digital image sensor for imaging and the solid state light emitting devices for lighting.
2. Description of the Prior Art
Several portable contact eye imaging systems have been proposed to photograph the posterior of human eyes (fundus camera) over the years. One of such, as disclosed in U.S. Pat. No. 5,608,472, is confined to use a fiber optical cable to guide the light from a remote light source to a hand held camera, which avoids the heat generated from the high brightness light source. The extension of the fiber cable also forms a circular light illumination device in order to distribute the light uniformly on to the posterior of an eye, as shown in FIG. 1. The details of the fiber optical ring structure are demonstrated in FIG. 2, where the fibers are tightly wrapped around and glued to the imaging optical lens where its exterior surface is tapered off. One of surfaces from the front lens is designed to contact the cornea of the eye with its radius matched to that of the cornea. The end of the concentric fiber ring and the matrix material are grounded and polished to have same radius as that of the contact surface of the front lens. The second embodiment in the FIG. 2, shows a more elaborated design where two concentric fiber rings are implemented with the purpose of increasing the distribution of light to the posterior of the eye, and extending the illuminated area by using different projection angles. However, such design has exhibited its unique difficulty in the manufacturing process and was not materialized in the real products. The improvement for the manufacturability was proposed in the U.S. Pat. No. 5,822,036 later, where a cornea contact glass lens is introduced and bonded to the original front lens, as shown in FIG. 3. The larger size of such contact lens not only provides protection for the fiber optical lighting apparatus, but also allows the use of the light conditioning optics, like Fresnel lens, to control the direction and distribution of the light to the posterior of the eye. The corneal contact lens, which forms a triplet with other two imaging lenses behind it, is then sealed to the shell of the imaging apparatus through its outer edge. Although the improvement in the design is significant, it also comes with its own problems, including for example the limitation on the design of light conditioning optics and the difficulty in achieving reliable sealing for the contact optics. A design for the imaging optics is also proposed in the U.S. Pat. No. 5,822,036, where the light from the posterior of the eye is collected by the contact triplet lens and several imaging lenses behind it to form a secondary image, as shown in FIG. 4. Additional relay optics, which is movable for adjusting the focus of the images, is used to directly form a real image from the secondary image plane onto an imaging sensor, like CCD. Such design is suitable for an imaging apparatus built with rather large imaging sensor, where the size of the imaging optics and the difficulty in making such small optics are not obstacles. However, when a miniature image sensor, together with its special imaging optics, is used in a complex imaging system, a new approach for the optical design must be taken.
In this invention, a new optical imaging apparatus, which is more reliable and portable, is proposed. It will be built with new generation of miniature digital cameras as its core imaging sensors and the high power solid state light emitters as its source.